This invention relates to particle-optical equipment for the irradiation of the surface of a solid material in massive form, or for the irradiation of a thin layer which can be penetrated by the radiation, both being described as the specimen or specimen surface in the following text. In this context, the invention relates particularly to those types of particle-optical equipment which are intended to apply an irradiation dose over a zone of the specimen surface which is large in comparison to the beam diameter and this surface zone may, for example, have a rectangular shape. To achieve this, it is essential that the beam be deflected from its original path and passed across the surface to be irradiated, by means of deflecting fields.
Such types of particle-optical equipment are, for example, employed in the production of highly integrated semiconductor circuits, most particularly when the dimensions of the circuit details approach, as the scale of integration is increased, the order of magnitude of the wavelength of light and, due to the unavoidable diffraction of light, photolithographic processes encounter their limit. Electron-beam lithography represents such a possibility of producing still finer structures. With this particle-optical process, the wavelength is so short that diffraction can, for practical purposes, be ignored when recording the structure details. So that both the special doping of the extremely finely structured regions of the semiconductor surface layer can be effected and the connecting conducting tracks can be produced, it is important, in the case of electron-beam lithography, to restrict the electron irradiation to the surface regions that are to be exposed, particularly concerning not only the dimensions and form of these regions but also their precise position on the semiconductor wafer. For this purpose, the places to be exposed, in the form of a closely spaced raster, are swept by a very fine focussed electron beam.
All of the locations to be irradiated lie in or in close proximity to a common plane which is oriented perpendicular to the axis of the electron beam irradiation instrument. This common plane is called the working plane.
The above procedure creates very onerous requirements with regard to precise adherence to the deflection angle necessary at any instant, according to which angle the electron beam is aimed at the places on the specimen surface to be irradiated. One of the problems occurring in this connection is caused by the chromatic aberrations of the deflection systems. Thus, if the deflecting magnetic field or the deflecting electric field is held constant, the deflection angle decreases as the velocity and energy of the particles increase. If the particle beam contains a finite range of energies, even if its energy spread is small compared with the beam energy, the deflection angle will accordingly extend over a correspondingly finite range. Analogously, the impact point of the particle beam, in the working plane or on the luminescent screen, will be deformed into a short line, lying in the direction of the deflection. In the case of electron-beam lithography machines, this effect leads, for example, to an increase in the width of the exposed lines and thereby leads to a limitation of the particle-optical performance capability, namely to a reduction in the resolving power, this reduction becoming particularly noticeable in the case of line widths below 1 .mu.m.
Now, it is usual up to the present to employ either exclusively magnetic or exclusively electric deflection systems, the decision in favor of one of the deflecting fields not normally being conditioned by electron-optical considerations alone, but by other technical factors often playing an important part, such as, for example, the availability of space, or the capability, with regard to the deflection system electric power supply, to handle signals in rapid sequence. For this reason, electric and magnetic deflection systems have also been employed simultaneously in some cases, in which the intrinsically slower magnetic deflection system provided the main part of the desired deflection, whilst a comparatively small but rapid electric deflection effected the fine-positioning of the beam with a high point sequence frequency. In these cases, the electric deflection, which typically equals only a few percent of the magnetic deflection, can be directed in the same sense as the magnetic deflection, or in opposition to it, and the two deflection angles do not remain in a fixed mutual relationship, either with regard to their directions or their magnitudes, which factor is, however, characteristic of the present invention.